FIG. 1 is a schematic illustration of a top plan view of a translating electronic registration system (TELER). Such systems are generally known in the art. See, for example, U.S. Pat. No. 5,094,442, herein incorporated by reference in its entirety.
The registration system 10 places a sheet S of media into proper alignment or registration for downstream processing as the sheet travels in the direction shown by arrow F. The registration unit 10 includes a carriage 12 having two drive rolls 14 and 16 rotatable mounted thereon by suitable means. The drive rolls 14 and 16 are driven by drive motors 18 and 20, respectively. The drive motors 18 and 20 are preferably speed controllable stepper motors, although other types of speed controllable servo motors are usable. The rotary output of each motor 18, 20 is transmitted to the respective drive roll 14, 16 by suitable power transmission means, such as shafts or belts.
Nip rolls (not shown) are mounted above drive rolls 14, 16 to engage the sheet S and drive it through the registration unit 10. The carriage 12 is mounted for movement transversely of the direction of feed indicated by arrow F. The carriage 12 is moved transversely of the feed path by a drive system including a speed controllable stepper motor 40 or other similar speed controllable servo motor. The output shaft of the motor 40, for example, drives a lead screw 42 connected to the carriage 12.
The registration system includes detectors for detecting the position of the sheet with respect to the registration system. Preferably, the sensors are optical detectors (photosensors) which will detect the presence of edges of the sheet S. For lead edge detection of the sheet, two sensors 48 and 50 are mounted on the carriage 12 adjacent the drive rolls 14 and 16 respectively. The detectors 48 and 50 detect the leading edge of the sheet S as it is drives past the sensors. The sequence of engagement of the sensors 48 and 50 and the amount of time between each detection is utilized to generate control signals for correcting skew (rotational mispositioning of the sheet about an axis perpendicular to the sheet) of the sheet S by variation in the speed of the drive rolls 14 and 16.
For lateral edge detection, a sensor 52 is suitably mounted and arranged on the registration unit 10 to generate control signals for correcting for lateral misregistration of the sheet S by moving the carriage 12.
Signals from the edge sensors 48, 50, 52 are provided to a controller 100. The controller 100 can be a typical microprocessor which is programmed to calculate correction values required and provide control outputs for effecting appropriate action of the stepper motors 18, 20 and 40. Such microprocessor control systems are well known to those of skill in the art and no detailed description thereof is necessary. Outputs of the microprocessor are provided controlling speeds and duration of drive of stepper motors 18, 20 and 40. Suitable driver control circuits are known in the art and no further detailed explanation is necessary.
A typical operating sequence for the registration system is as follows. For purposes of this analysis, the roll drive and translation motion are all assumed to take place with constant accelerations. The drive rolls 14 and 16 are initially driven at the same constant speed. The skew sensor 48 and 50 first detect the leading edge of the sheet S. Depending upon the direction of skew detected by sensors 48 and 50, the speed of roll 16 is increased or decreased, while the speed of roll 14 is correspondingly decreased or increased in the same time period. Once the skew position of the sheet has been achieved, the carriage translating motor 40 is driven to effect lateral edge positioning.
The sheet must also be laterally registered. This lateral registration is the result of first identifying where the sheet is and then moving the sheet laterally to some target edge location. The basic logic of lateral registration operation provides that, if the sensor 52 is covered by the sheet, the motor 40 will be controlled to move the carriage 12 laterally a distance that the sensor 52 is covered by the sheet S.
A difficulty lies in accurately identifying how the skew error of the sheet affects the lateral position during registration. For example, the drive rolls 14 and 16 may not be able to correct for skew entirely. As such, there still may be a very small skew error depending on the machine tolerances. Furthermore, as improvements upstream of the registration unit 10 decrease the initial lateral misregistration of the sheet, the lateral component of the skew error may become a more significant portion of the total error during lateral registration.